Optical fibres generally comprise filaments of optically transparent, non-ductile, "glassy" materials, for example vitreous silica, boro-silicate, or metal fluoride glasses. To enable guided transmission to take place, the fibres require a core and a cladding. Occasionally the function of the cladding may be performed by, for example, the surrounding air. In practice, however, optical fibres employed to transmit information usually have cores and claddings.
Different types of optical fibre will have different dimensions associated with them but, generally, the outer diameter varies (with fibre type) over a range of from 60 .mu.m to 250 .mu.m.
When optical power is to be transmitted into or out of the end of an optical fibre, the giometric characteristics of the fibre end affect the manner in which the power is transmitted. It is often desirable that the fibre should be provided with a flat end face which lies perpendicular to the longitudinal axis of the fibre. For instance if two fibres for use in optical communications are fusion jointed, it is known that if either end face is not perpendicular, optical power loss can be significantly increased at the joint. For example, the two fibre ends may tend to ride past one another during making of the joint, leading to misalignment of the fibres. Where a major part of the optical power is carried by a fibre core this power loss can be substantial and monomode fibres are known to be particularly susceptible as a result of their small core diameters. Typically these are about 8 .mu.m in a fibre whose overall diameter including core and cladding is in the region of 125 .mu.m.
An acceptable fibre end face can be obtained by clamping the fibre under a controlled axial tension, free from any torsional strain, and striking it on its outermost glass surface with a cleaver blade. In known cleaving tools the cleaver blade may be mounted in a sliding cleaver which is propelled along a horizontal bearing surface to bring the blade into contact with the fibre. Alternatively the blade may be mounted on a lever which drops under the influence of gravity to bring the blade into contact with the fibre.
Problems of reliability have been encountered with such arrangements. For instance, the action of both types of arrangement can be extremely sensitive to changes in orientation, or to movement, of the cleaving tool.